Impeller weld restraining fixture

ABSTRACT

The present invention provides an apparatus for use in automated welding repairs, particularly those repairs intended for impellers and similar structures. In one embodiment, the invention provides an impeller weld restraining fixture. The fixture includes a base plate and top ring. An impeller may be sandwiched between the base plate and the top ring. Tangs located on the top ring may be fitted to rest in the valley faces between airfoils on an impeller. Bolting the top ring to the base plate, with the impeller firmly secured therebetween, restrains the impeller so as to minimize warpage during welding repairs and heat treatments.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.11/044,868, filed on Jan. 26, 2005 now U.S. Pat. No. 7,469,452.

FIELD OF THE INVENTION

The present invention relates to welding repairs for impellers. Moreparticularly the invention is related to a fixture used to maintainproper impeller geometry during welding and repair operations.

BACKGROUND OF THE INVENTION

Turbine engines are used as the primary power source for many types ofaircrafts. The engines are also auxiliary power sources that drive aircompressors, hydraulic pumps, and industrial gas turbine (IGT) powergeneration. Further, the power from turbine engines is used forstationary power supplies such as backup electrical generators forhospitals and the like.

Most turbine engines generally follow the same basic power generationprocedure. Compressed air generated by axial and/or radial compressorsis mixed with fuel and burned, and the expanding hot combustion gasesare directed against stationary turbine vanes in the engine. The vanesturn the high velocity gas flow partially sideways to impinge on theturbine blades mounted on a rotatable turbine disk. The force of theimpinging gas causes the turbine disk to spin at high speed. Jetpropulsion engines use the power created by the rotating turbine disk todraw more air into the engine and the high velocity combustion gas ispassed out of the gas turbine aft end to create forward thrust. Otherengines use this power to turn one or more propellers, fans, electricalgenerators, or other devices.

Low and high pressure compressor (LPC/HPC) components such as compressorblades and impellers are primary components in the cold section for anyturbine engine, and are typically well maintained. The LPC/HPCcomponents may be subjected to stress loadings during turbine engineoperation, and also may be impacted by foreign objects such as sand,dirt, and other such debris. The LPC/HPC components can degrade overtime due to wear, erosion, foreign object damage, and other factors.Sometimes LPC/HPC components are degraded to a point at which they mayneed to be repaired or replaced, which can result in significantoperating expense and time out of service.

There are several traditional methods for repairing damaged turbineengine components, and each method has some limitations in terms ofsuccess. One primary reason for the lack of success is that thematerials used to make LPC/HPC components do not lend themselves toefficient repair techniques. For example, titanium alloys are commonlyused to make impellers because the alloys are strong, light weight, andhighly corrosion resistant. However, repairing an impeller withconventional welding techniques subjects the impeller to hightemperatures both during the welding operation and during any pre- orpost-welding heat treatment. This high temperature has resulted inwarpage to impeller structures.

Nevertheless, there is a continuing need for improved repair methodsthat allow quicker repairs that minimize the need to scrap expensiveparts. The modern jet aircraft is a very high capital thing. Gas turbineengines, for example, include many expensive components with complexshapes; impellers are one example of such a component. The complexdesign, and expensive materials, that are used to fabricate impellersoften means that they can be quite expensive. As a consequence of thesedesign and material criteria, it is desirable to repair damagedimpellers when possible. The geometry of turbine engine impellers makesthem particularly vulnerable to heat-related warping. The challenge isto heat the part to the temperatures needed for welding repair whileretaining the part's geometry.

Accordingly there is a need for an apparatus and method to protectimpellers from welding damage that arises from high temperatures. It isdesired that the apparatus be able to prevent excessive warping of theimpeller shape. Further, it is desired that the apparatus, and method ofusing the apparatus, be suitable for use with automated welding systems.It is thus desired that the efficiency of automated welding systems notbe unduly compromised by the protective apparatus and method. Thepresent invention addresses one or more of these needs.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and methods for use inautomated welding repairs. In one embodiment, the invention provides animpeller weld restraining fixture. The fixture includes a base plate andtop ring. An impeller may be sandwiched between the base plate and thetop ring. Tangs located on the top ring may be fitted into the spacesbetween blades on a turbine impeller or blisk.

In one embodiment, and by way of example only, there is provided afixture for use in weld repairing an impeller comprising: a base platestructured for restraining an impeller; and a top ring structured forrestraining an impeller wherein the top ring may be attached to the baseplate such that an impeller is firmly held between the base plate andtop ring when the top ring is attached to the base plate. The base plateand top ring may be fabricated of nickel alloys such as AMS 5596. Thebase plate may include a surface for receiving the curvic face of animpeller, and the top ring may have a number of tangs that contactvalley faces of the impeller. The number of tangs may or may not matchthe number of valley faces of the impeller. Further, the top ring andbase plate may have a number of matching holes such that nuts and boltsthat may be disposed through these matching holes so as to firmly holdthe top ring and base plate together. The number of matching holes mayor may not equal the number of valley faces of the impeller, and thenuts and bolts may be formed of a nickel-based Inconel alloy such asInconel 718.

Other independent features and advantages of the impeller weldrestraining fixture will become apparent from the following detaileddescription, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a gas turbine engine impeller such asmay be used with the present invention;

FIG. 2 is a cross-section of a gas turbine engine impeller as may beused with the present invention;

FIG. 3 is an exploded view of a weld restraining fixture according to anembodiment of the present invention;

FIG. 4 is a perspective view of a base plate, according to an embodimentof the present invention;

FIG. 5 is a cross section view of a base plate, according to anembodiment of the present invention;

FIG. 6 is a perspective view of a retraining ring according to anembodiment of the present invention;

FIG. 7 is a cross section view of a retaining ring according to anembodiment of the present invention;

FIG. 8 is a cross section view of a restraining fixture assembled withan impeller, according to an embodiment of the present invention; and

FIG. 9 is a flow chart showing steps in an impeller repair process thatuses the restraining fixture, according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit the invention or the applicationand uses of the invention. Furthermore, there is no intention to bebound by any theory presented in the preceding background of theinvention or the following detailed description of the invention.Reference will now be made in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

It has now been discovered that welding repairs on gas turbine engineimpellers can be improved through the use of a weld restraining fixture.As described further herein, an embodiment of a weld restraining fixtureincludes a base plate and top ring that may be affixed to the base plateso as to secure an impeller therebetween. In a preferred usage of thewelding fixture, an impeller is secured to the fixture and remains thereduring welding steps including welding, heat treatment, and optionally,post-welding surfacing operations.

Referring now to FIG. 1 there is shown a representation of a typicalimpeller suitable for use with the present invention. Impeller 10includes a plurality of impeller airfoils 11 attached to a central core12. Impeller 10 has a generally radial structure and, as shown in thisfigure, a central bore area 13. In some designs, impeller 10 isfabricated as a unitary piece with an axle and would not have an openbore area, though it would have the corresponding bore region. Centralbore area 13 is aligned along an imaginary central axis 14 that runsthrough central bore area 13 in an axial direction. In operation,impeller 10 is disposed on a central axle (not shown) at central borearea 13 and rotates thereon or rotates with the axle. Impeller blades 11extend from central bore area 13 in an outwardly radial and axialdirection. Impeller 10 further defines an upstream position 15 anddownstream position 16. Upstream position 15 and downstream position 16correspond to the fluid path flow through and across impeller 10. Fluid,such as air, first enters impeller 10 at the upstream position 15(inducer). As air passes impeller 10 it exits in the downstream position(exducer). Air passing across impeller 10 is pressurized such that theair exiting impeller 10 is at a higher temperature and pressure relativeto the air entering impeller 10. The direction of air flow 17 is acrossthe face of impeller 10, the face being that portion of impeller 10which is exposed to air flow. In operation, impeller 10 is disposedwithin a housing or structure (not shown) which, by close proximity toimpeller blades 11, assists in placing the air under pressure.

An individual airfoil 11 may further be described as defining a contouredge 20. Contour edge 20 is the generally ridge-like surface thatextends in height from airfoil 11. Additionally each airfoil 11 definesa pressure face 21 and a suction face 22. Pressure face 21 is that faceof airfoil 11 that spins into the air being compressed when an airfoilrotates. Suction face 22 is the opposite face of the airfoil 11.Neighboring airfoils define a valley 23 therebetween. It can also bestated that valley 23 is bounded by neighboring airfoils. As used inthis specification, the term “valley” refers to the empty space, orvolume, that is defined between two neighboring airfoils on an impelleror blisk. The valley face 24 is that portion of the impeller or bliskstructure that lies between neighboring airfoils. Thus the valley face24 forms a bottom boundary of a valley 23. Similarly a pressure face 21of an airfoil forms a boundary of a valley, and a suction face 22 formsanother boundary of a valley. By the open nature of the impeller/bliskstructure, there is no upper boundary on a valley 23. Similarly, thevalley is unbounded at the inducer and exducer positions.

Referring now to FIG. 2 there is shown a cross section view of animpeller. This view also illustrates curvic face 25 of the impeller,which was hidden in FIG. 1. Curvic face 25 is included on many impellerdesigns. It is a projection that may include toothed or gearedstructures. Curvic face 25 is generally symmetrical about central axis14. As explained further herein, curvic face 25 is involved inpositioning impeller 10 on the restraining fixture.

Referring now to FIG. 3 there is shown an exploded view of a restrainingfixture, according to an embodiment of the present invention. Therestraining fixture in FIG. 3 also has an impeller positioned ready tobe restrained in the fixture. The restraining fixture includes baseplate 31 and top ring 32. Further illustrated in FIG. 3 are bolts 33 andnuts 34, representing one method of affixing top ring 32 to base plate31. An exemplary impeller 35 is shown disposed between base plate 31 andtop ring 32 where, for example, impeller 35 may be secured.

Referring now to FIG. 4 there is shown a perspective view of anexemplary embodiment of base plate 31. Base plate 31 includes a firstsurface 36 and second surface 37. In a preferred embodiment, firstsurface 36 and second surface 37, which are concentric, are generallycircular in shape. Base plate 31 further includes annular surface 38.Holes 39 in annular surface 38 extend through the thickness of baseplate 31 and may be employed with nuts and bolts to fasten base plate 31to top ring 32. Holes 39 are preferably aligned along the same radiusrelative to the center of base plate 31.

It is noted that base plate 31 is generally circular in its outer shapeas shown in FIG. 4. This is a preferred shape for material savings andfor ease of handling; however, it is noted that the outer shape of baseplate 31 may assume other shapes or configurations.

FIG. 5 is another illustration of base plate 31. FIG. 5 provides a crosssection view which illustrates, for example, the comparative depths offirst surface 36 and second surface 37, according to one embodiment ofthe base plate 31. Thus, as is shown, second surface 37 is deeper thanfirst surface 36, relative to annular surface 38.

Referring now to FIG. 6 there is shown a perspective view of anexemplary embodiment of top ring 32. As shown, top ring 32 is agenerally circular structure that defines a central opening 41. Acentral axis of top ring 32 may be defined within central opening 41.Again, the overall shape of top ring 32 is preferably circular in orderto realize a material savings and to allow ease of handling, but othershapes are possible. Top ring 32 further includes top surface 45 andbottom surface 42 (shown in FIG. 7). Bottom surface 42 is preferablyplanar. Holes 43 are also present in top ring 32 in a preferredembodiment. Holes 43 of top ring 32 are designed to align with holes 39in a corresponding base plate 31.

Still referring to FIG. 6, top ring 32 includes tangs 44. Tangs 44project into central opening 41 toward the central axis of top ring 32.Tangs 44 extend radially inwardly from top ring 32. Tang 44 provides astructure by which material of top ring 32 is projected such that thebottom surface 42 of top ring 32 is further extended by tangs 44 intothe area of the central opening 41. As will be further explained, thisprojection by tangs 44 allows top ring 32 to mate with valley face 24 ofan impeller in order to secure the impeller to base plate 31. FIG. 7provides a cross section view of top ring 32, and it illustrates manycommon features.

The shape of tangs 44 may vary. However, it is preferred to fabricatethem substantially in the shape shown in FIG. 6. In this embodimentbottom surface 42 extends in planar relation along the tang structure. Aprojection surface 46 of tang 44 is formed by a surface extending fromupper or top surface 45 of top ring 32 along the tang structure. Asshown in FIG. 6 it is preferred that projection surface 46 is set atsome angle different from the plane of upper surface 42. Whileprojection surface 46 is shown in the preferred embodiment assubstantially straight, other embodiments are also possible. Tangs 44may be fabricated by cutting material away from top ring 32 duringmanufacturing. For example, radial or circular cuts may define the shapeof tangs 44. One feature of tang 44 is its width 47. As is discussedfurther below, top ring 32 is positioned on an impeller so that tangs 44rest on valley faces 24 of impeller. Thus, the width 47 of tang 44should be selected to allow this positioning. Tang 44 should notinterfere with airfoils 11 that neighbor a valley 23.

In a preferred embodiment, a top ring 32 includes a tang 44 for eachvalley 23 of an impeller with which that top ring 32 is to be used.However, in other embodiments, different numbers of tangs 44 may beprovided. Similarly, in a preferred embodiment, top ring 32 and baseplate 31 have corresponding holes 39, 43 that match the number ofvalleys 23 in the impeller to be secured. However, in other embodiments,the number of holes 39, 43 may be different than the number of valleys23.

In a preferred embodiment, components of the weld restraining fixtureare made of high-strength materials sufficient to withstand bending andshear forces that are generated in assembling the fixture. Preferablybase plate 31 and top ring 32 comprise the same or similar metal alloy.In a preferred embodiment, base plate 31 and top ring 32 are fabricatedof a nickel alloy known by SAE designation AMS 5596. An exemplarycontent of such an alloy is as follows, by weight percent.

Element min. max. Carbon — 0.08 Manganese — 0.35 Silicon — 0.35Phosphorus — 0.015 Sulfur — 0.015 Chromium 17.00 21.00 Nickel 50.0055.00 Molybdenum 2.80 3.30 Columbium 4.75 5.50 Titanium 0.65 1.15Aluminum 0.20 0.80 Cobalt — 1.00 Tantalum — 0.05 Boron — 0.006 Copper —0.30 Iron remainder

In this kind of embodiment, the titanium material of a titanium-alloyimpeller is softer than the nickel alloy that constitutes top ring 32and base plate 31. Thus, the nickel alloy base plate 31 and top ring 32are able to restrain the softer titanium-alloy impeller. When nuts andbolts are used as the means to secure base plate 31 and top ring 32, itis preferred that they be formed of Inconel type nickel alloys.

Having described the invention from a structural standpoint, a methodand manner of using the invention will now be described.

Once an impeller is identified for repair, it is prepared for welding,or other kind, of repair. This may include procedures known in theindustry such as grit blasting and degreasing. At this point, impeller10 is ready to be secured in the restraining fixture. The restrainingfixture is disassembled so as to receive impeller 10. It is alsopreferred that the components of the restraining fixture, such as baseplate 31 and top ring 32 also be clean.

Impeller 10 is first positioned to rest on base plate 31. The assemblyis such that it may be achieved by hand. This is done such that curvicface 25 rests on second surface 37 of base plate 31. Base plate 31 issized so that, when impeller 10 rests on base plate 31, the outer radialedge of impeller 10 overlaps with annular surface 38 of base plate 31.This overlap can be seen in FIG. 8. FIG. 8 illustrates a cross sectionview of an impeller held in a restraining fixture. At this point,impeller 10 rests on its own weight on base plate 31. Depending on thedesign, impeller 10 may contact or may not contact annular surface 38 ofbase plate 31. In a preferred embodiment, impeller 10 does not contactannular surface 38 when impeller 10 only rests on base plate 31.

At this point, top ring 32 may be secured and affixed to base plate 31.Top ring 32 is positioned on impeller 10 so that tangs 44 rest on valleyfaces 24 of impeller 10. It is preferred that tangs 44 be centeredwithin each valley face 24. Additionally, top ring 32, and impeller 10,may be rotated in order to align holes 43 of top ring 32 with holes 39in base plate 31. Bolts 33 may be disposed within holes 43, 39 andsecured to nuts 34. Both top ring 32 and base plate 31 are configured toengage a particular impeller design.

It is desired to secure impeller 10 between base plate 31 and top ring32. This is achieved by torqueing bolts 33 and nuts 34. The degree oftorqueing accordingly plays a role in securing the impeller. It is thuspreferred that the torqueing be to a minimum of 30 foot-pounds (ft-lbs).

As a result, when the impeller is loaded into the fixture and thefixture is torqued to a desired amount, it is the impeller that does themajority of the bending, rather than the fixture doing the bending.Referring now to FIG. 8, there is shown an assembled restrainingfixture. In this illustration, top ring 32 has been fully assembled tobase plate 31, and impeller is thereby restrained. It is noted that, atthis point in the assembly process, impeller 10 is in contact with bothbase plate 31 at annular surface 38 and top ring 32 at bottom surface 42of tangs 44. Additionally, there is a gap 50 between top ring 32 andbase plate 31. In this embodiment, fully torqueing top ring 32 to baseplate 31 does not result in those pieces contacting each other.

The preferred embodiment of the restraining fixture has described bolts33 and nuts 34 as the means by which to firmly affix top ring 32 andbase plate 31. Other mechanisms may be used to achieve this coupling,including, for example clamps.

Once the impeller 10 is restrained by the top ring 32 and base plate 31,the impeller may be repaired. One such repair includes welding andresurfacing of airfoil edges. It is preferred that the impeller 10remain in the restraining fixture during welding operation and postwelding heat treatment operations. Additionally, it is preferred to keepthe impeller positioned in the restraining fixture during any grindingor finishing operations.

Thus, one embodiment of a welding operation to repair an impeller edgesurface includes the following steps, illustrated in FIG. 9. In step 90an impeller is prepared for welding. This may include degreasing andgrit blasting the impeller. The preparation step may also includeselection and inspection of the impeller such that impellers that cannotbe weld repaired are identified and removed.

In step 91 the impeller is placed in the restraining fixture. In thisstep the impeller is placed onto base plate 31. The top ring 32 is thenpositioned onto the impeller and connected to base place 32. Top ring 32and base plate 31 are then connected to a desired force such that theimpeller is firmly held in the restraining fixture.

At this point, step 92, the impeller may receive a weld repair. Thisincludes, among other operations a surface or edge restoration. Atypical weld repair includes TIG welding of an airfoil edge. Followingthis, the impeller may be subject to a heat treatment, step 93.

At this point, step 94, the impeller may be removed from the restrainingfixture. This includes unbolting top ring 32 and base plate 31. Theimpeller is then removed from those pieces.

Following the heat treatment, the impeller may receive a finishing orgrinding, step 95. Finishing and grinding step 95 restores airfoilsurfaces to a final geometry. The impeller may then be inspected andreturned to service.

Repairs made to impellers with the weld restraining fixture haveresulted in impellers having an improved finished geometry. Oneimprovement that is noted in those impellers restrained by embodimentsof the restraining fixture relates to variance in radial warp of theimpeller. Impellers can be characterized by a dimension “Y” shown inFIG. 2. Dimension Y denotes the distance between a point on the outerradial edge of the impeller, and a plane extending from curvic face 25.In prior art repairs, it has been observed that a “potato chip” effectoccurs. That is dimension Y differs at various radial points of theimpeller. In particular, points at an impeller valley may have differentY dimensions compared to those points measured at the airfoil. Thus,there is a wave, or potato chip, look to those impellers. This effect isundesirable because an overly large variance in Y dimension candisqualify an impeller from return to service. Exemplary weld repairshave been achieved where the Y dimension variance is approximately 0.001to 0.002 inches. This is contrasted with repairs performed without therestraining fixture having a variance of approximately 0.010 inches.Hence, repairs with the weld restraining fixture have achievedapproximately an order of magnitude improvement.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt to a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodiment disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe appended claims.

1. An assembly for weld repairing an impeller comprising: a base platehaving an annular surface and a resting surface; an impeller having acurvic face and a plurality of valley faces, wherein the impeller ispositioned on the base plate so that the curvic face of the impellercontacts the resting surface of the base plate; a top ring having aplurality of tangs, wherein the top ring is positioned on the impellersuch that the tangs of the top ring contact the plurality of valleyfaces of the impeller; and means for coupling the top ring to the baseplate to thereby restrain the impeller therebetween.
 2. The assemblyaccording to claim 1, wherein the means for coupling comprises aplurality of nuts and bolts.
 3. The assembly according to claim 2,wherein the plurality of nuts and bolts comprise the alloy Inconel 718.4. The assembly according to claim 1, wherein the top ring is bolted tothe base plate.
 5. The assembly according to claim 1, wherein the topring is bolted to the base plate at a torque of at least approximately30 ft-lbs.
 6. The assembly according to claim 1, wherein the base plateand top ring comprise the same nickel-based alloy.
 7. The assemblyaccording to claim 1, wherein the base plate and top ring comprise thesame alloy which is an alloy with greater strength than the strength ofthe impeller being repaired.
 8. The assembly according to claim 1,wherein the means for coupling comprises at least one clamp.